The technology of and techniques for testing the visual acuity of infants, other young children and the functionally young (handicapped) have been the subject of considerable research over the past five to ten years, and one relatively recently developed technique known as "The Acuity Card Procedure" has been found to make it possible to estimate the visual acuity of normal infants with reasonable accuracy in a few minutes in a laboratory setting.
In testing a child by this procedure, the child sits or is held in front of a screen containing a test card having thereon a black and white grating and a blank target of the same space-average luminance as the grating. The child is shown a number of presentations of gratings of different spatial frequencies, with the left-right location of the grating varied from one presentation to the next. The observer judges the visual acuity of the child by noting the eye and head movements of the child in response to each presented test card, through a peephole in the card.
In the preferred practice of the acuity card procedure, the person holding the child is shielded from the position where each of the successive cards is presented in order to prevent such person from consciously or unconsciously influencing the child's reactions to the cards. For this purpose, provision may be made to locate a shield between the eyes of that person and the position of card presentation.